borrowenum.rs

extern mod std;

use std::map::HashMap;
use std::map::Set;
use std::map::vec_from_set;

enum Choice {
    Many(Set<int>),
    One(int),
}

fn main() {
    let choices: ~[mutable::Mut<Choice>] = ~[mutable::Mut(Many(HashMap()))];
    for vec::each(choices) |choice| {
        let result = do choice.borrow_imm() |choice| {
            match *choice {
                Many(opts) if opts.size() == 1 => Some(vec_from_set(opts)[0]),
                Many(_) | One(_) => None
            }
        };
        do option::iter(&result) |result| {
            do choice.borrow_mut() |choice| {
                *choice = One(*result);
            }
        }
    }

    log(error, choices);
}

stderr

borrowenum.rs:17:17: 17:22 error: illegal borrow unless pure: enum variant in aliasable, mutable location
borrowenum.rs:17             Many(opts) => {
                                  ^~~~~
borrowenum.rs:19:20: 19:27 note: impure due to assigning to dereference of mutable & pointer
borrowenum.rs:19                     *choice = One(vec_from_set(opts)[0]);
                                     ^~~~~~~
error: aborting due to previous error